Thermal substrate with high-resistance magnification and positive temperature coefficient ink

ABSTRACT

An article comprising a heater that comprises a high-resistance magnification (HRM) PTC ink deposited on a flexible substrate to form one or more resistors. The HRM PTC ink has a resistance magnification of at least 20 in a temperature range of at least 20 degrees Celsius above a switching temperature of the ink, the resistance magnification being defined as a ratio between a resistance of the double-resin ink at a temperature ‘T’ and a resistance of the double-resin ink at 25 degrees Celsius.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 17/034,653 filed Sep. 28, 2020, which is a continuation of U.S.patent application Ser. No. 16/041,076 filed Jul. 20, 2018, now U.S.Pat. No. 10,822,512, which is a continuation-in-part of U.S. patentapplication Ser. No. 15/143,524, filed Apr. 30, 2016, now U.S. Pat. No.10,077,372, which claims the benefit of U.S. Provisional Application No.62/389,396, filed Feb. 24, 2016, each of which is hereby incorporated byreference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to the field of PTC inks. It relates toapplications that use PTC inks exhibiting switching characteristics,high resistance magnification and the delayed onset of NTC behavior in atemperature range relevant to a particular application.

BACKGROUND

The terms positive temperature coefficient (PTC) materials and positivetemperature coefficient of resistivity (PTCR) materials, as used herein,refer to materials that increase resistivity nonlinearly when theirtemperature is raised. Reference may be made, for example, to U.S. Pat.Nos. 4,628,187, 5,181,006, 5,344,591, and 5,714,096, and Japanese PatentPublication Nos. 2008293672, 2009151976, and 2009199794. The temperaturewhere the resistance increases nonlinearly, thereby reducing current, isreferred to herein as the switch temperature.

Polymers can be made electrically conductive by dispersing suitableamounts of conductive particles such as carbon black or fine metalparticles. A sub-class of electrically conductive polymers can be madeto exhibit PTC behavior. Polymeric compositions exhibiting PTC behaviorand devices incorporating the same have been used in many applications,especially in the electronics industries. A common use in an electroniccircuit is limitation of current which is controlled by the temperatureof a PTC element forming part of the circuit. An increasing use of PTCmaterials is for constant temperature heaters.

However, carbon-based polymeric PTC materials suffer from severalimportant operational technical problems. For example, most PTCcompositions exhibit Negative Temperature Coefficient (NTC)characteristics of resistivity immediately after the PTCcharacteristics. This change from PTC behavior to a strong NTC behavioris often undesirable and may cause self-burning in some cases. The lowerresistance at the onset of NTC leads to excessive current flow and theresistor, or heater, is overpowered. Therefore, the NTC temperatureregion is a potential safety-risk temperature region. Various effortshave been made to reduce the NTC effect as described in U.S. Pat. Nos.8,496,854 and 5,227,946 and European Pat. EP 0311142. However, the NTCeffect is only reduced and not eliminated.

Another problem with current polymeric PTC materials is a low resistancemagnification at the switch temperature, typically ranging from 5-15.This results in some power dissipation even at maximum resistance whichresults in poor temperature regulation.

Another problem is the transition temperature region between the lowresistance state and the high resistance state where only partialcurrent flows. The transition region varies in width proportional toambient temperature and the overall conditions for heat transfer.Therefore, the operational characteristics of the heater are determinedby many design factors involving its physical environment. This affectsthe heater's power dissipation, the time-to-switch and the heater's holdcurrent.

Still another problem is that many PTC materials exhibit resistancehysteresis when switched. This is observed as a partial resistanceincrease over the starting resistance even hours after the switch event.In time, the original resistance is approached but it may be days,months, or years. Fortunately, the resistance is not cumulative oversubsequent switch events so strategies can be taken to account for thisphenomenon.

Yet another problem is the PTC material's resistance recovery time aftera reset event. The time is usually one to two minutes but can be longerdepending on the heat transfer environment of the heater and itsmaterial design.

One application for PTC inks is electrically heated fabrics.Electrically heated fabrics are used commonly in clothing for outdooractivities, medical devices, and some industrial applications. The termfabric as used herein refers to a woven material comprising threads oryarns or a non-woven material such as thermoplastic polyurethane whenused as part of a garment. One class of heated fabrics utilizes heatingelements of nickel-chromium or other resistive alloy in foil or wireform with a battery as a portable energy source. Another class usespolymer films with electrically conductive polymers deposited on a filmas described in U.S. Pat. No. 9,161,393 B2. In yet another class, Pat.No. CN 104,476,890 B describes printing directly on the fabric usingscreen printing.

In all cases but the last, the heating elements, placed adjacent to orattached to the fabric, typically provide non-uniform heat and developconstant power in the element. In the last case, the metal interconnectsare subject to bending and cracking thereby causing heater failure. Inall cases, conductive polymers that are not PTC require controls andwhen PTC inks are used, they are subject to NTC failure or burn outtogether with poor self-regulation due to their small resistancemultiplication.

Fabrics with heating elements woven like threads into the fabricconstitute yet another class. Wires have been woven into the fabric asdescribed in U.S. Pat. No. 1,703,005 A. In Pat. No. GB 2,092,868 A, ametallized woven fabric is described, its purpose being to solve theproblem of stretching. In most cases described, a simple voltageregulator adjusts temperature level with no feedback control. Also, thewoven wires are problematic for making good electrical connections. Theyare subject to damage because their small size is determined by theelectrical resistance necessary to generate low power and not therobustness of the fabric.

U.S. Pat. No. 7,151,062 B2 describes a woven fabric with yarns coatedwith conductive polymers including PTC ink comprising coated spheres.The PTC ink described is subject to the deficiencies of common PTC inksas described above. US '062 also claims wire conductors to serve asinterconnects cross-woven to the conductive yarns.

SUMMARY

In one aspect, there is disclosed a thermal substrate comprising asubstrate and a high-resistance magnification (HRM) PTC ink and asubstrate, wherein the HRM PTC ink that has a positive temperaturecoefficient (PTC) and a resistance magnification of at least 15 in atemperature range of at least 20 degrees Celsius above a switchingtemperature of the HRM PTC ink.

In another aspect, there is disclosed an article comprising a heater,the heater comprising a HRM PTC ink deposited on a flexible substrate toform one or more resistors; wherein: the substrate is thermalpolyurethane, nylon, or a polyester blend. The HRM PTC ink may bedeposited on to the substrate by screen printing. In some embodiments,the substrate is thermal polyurethane. In some embodiments, the heateris encapsulated by a dielectric ink or a thin film. The heater mayfurther comprise a plurality of conductive traces; the plurality ofconductive traces can be each silver traces.

In another aspect, there is disclosed a panel comprising an encapsulatedheater, the heater comprising: a double-resin ink having a positivetemperature coefficient (PTC) deposited on a flexible substrate to formone or more resistors, the double-resin ink comprising a first resincomprising a crystalline or a semi-crystalline polymer; and a secondresin comprising a non-crystalline polymer; wherein the substrate isthermal polyurethane; and the heater is encapsulated in a dielectricink. In some embodiments, the heater is encapsulated by a dielectric inkor a thin film. The heater may further comprise a plurality ofconductive traces; the plurality of conductive traces can be each silvertraces.

The resistance magnification of the HRM PTC ink may be at least 20, 30,40, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180 or 200. In addition, thetemperature range may be 25 degrees Celsius, 30 degrees Celsius, 35degrees Celsius or 40 degrees Celsius above the switching temperature.Furthermore, the switching temperature of the HRM PTC ink may be between0 and 160 degrees Celsius.

As an example, the HRM PTC ink may be a double resin ink that comprises:a first resin that provides a first PTC effect in a first temperaturerange; and a second resin that provides a second PTC effect in a secondtemperature range, wherein the second temperature range is higher thanthe first temperature range.

As an example, the double-resin HRM PTC ink may comprise about 10-30 wt% conductive particles; about 5-15 wt % of a first polymer resin; about5-15 wt % of a second polymer resin; about 40-80 wt % of an organicsolvent; and about 0-5 wt % other additives. The conductive particlescan be one of, or a mixture of: a metallic powder, a metal oxide, carbonblack and graphite. The first polymer resin may be a kind of crystallineor semi-crystalline polymer, such as polyurethane, nylon, and polyester.The second polymer resin may be a kind of non-crystalline polymer, suchas acrylic resin. The selection of the solvent is based on its properboiling point and the solubility of polymer resins since the polymerresins are completely dissolved in the organic solvent prior to blendingwith other components. Any organic, inert liquid may be used as thesolvent for the so long as the polymer is fully solubilized. Asexamples, the solvent may be selected from MEK, N-methyl pyrolidone(NMP), toluene, xylene, and the like. The other additives include adispersing/wetting additive and a rheology additive.

As an example of the double resin composition, the HRM PTC ink maycomprise about 5-15 wt % of a thermally active polymer resin-1 having amelting point of 30-70° C. and providing a first temperature coefficientcharacteristic in the first temperature range below 70° C.; about 5-15wt % thermally active polymer resin-2 having a melting point of 70-140°C. and providing a second positive temperature coefficientcharacteristic in the second temperature range above 70° C.; about 10-30wt % conductive particles; about 40-80 wt % organic solvent having aboing point higher than 100° C., the organic solvent being capable ofdissolve both the polymer resin-1 and polymer resin-2, and about 0-5 wt% additives. The additives may comprise dispersing additives, wettingadditives, and rheological additives, with the additives having enhanceddispersing/wetting and rheology properties. The first polymer resin maybe a kind of crystalline or semi-crystalline polymer, such aspolyurethane, nylon, and polyester. The second polymer resin may be akind of non-crystalline polymer, such as acrylic resin.

The thermal substrate may be a fabric, a mesh, or a film.

Furthermore, the HRM PTC ink may be deposited onto the substrate.Non-limiting examples of deposition method include screen printing, useof a thick film dispenser or a 3-D printer.

Where the substrate is a fabric or mesh, deposition of the HRM PTC inkmay provide a printed circuit with resistors in parallel. In this case,the thermal substrate may further comprise electrical interconnects thatcomprise at least one of a metal paste, a metal foil, a metal alloy,aluminum, copper, nickel, and a high-conductivity electronic polymer.

In other embodiments of the thermal substrate, the HRM PTC ink may bedeposited on at least one insulating thread, yarn or filament that isincorporated into a fabric or mesh. An insulator can seal the HRM PTCink.

In other embodiments of the thermal substrate, the HRM PTC ink may bedeposited on at least one conducting thread, yarn or filament that isincorporated into a fabric or mesh, with the HRM PTC ink sealed on anouter surface thereof with a conductor. An insulating layer may beapplied to the conductor.

In other embodiments, the substrate may be a film. The film may be apolymer selected from the group consisting of polyethylene terephthalate(PET), polyethylene (PE), aluminum and steel (for meshes), glasscomposite, molded plastic, high-density polyethylene (HDPE) and styreneethylene butylene styrene (SEBS). As with the other embodiments, thethermal substrate may comprise electrical interconnects that comprise atleast one of a metal paste, a metal foil, a metal alloy, aluminum,copper, nickel, and a high-conductivity electronic polymer. An optionallayer of a second film may be laminated onto the HRM PTC ink.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

The recitation herein of desirable embodiments is not meant to imply orsuggest that any or all of these embodiments are present as essentialfeatures, either individually or collectively, in the most generalembodiment of the present invention or in any of its more specificembodiments.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other advantages of the disclosure will becomeapparent upon reading the following detailed description and uponreference to the drawings.

FIG. 1 shows the relationship of the PTC ratio R_(T)/R₂₅ versustemperature T of a typical PTC composition.

FIG. 2 shows the relative resistance magnification of a high-resistancemagnification (HRM) PTC ink that exhibits an upper resistancemagnification greater than 200 above a temperature of 70 Celsius.

FIG. 3 illustrates an embodiment of a printed circuit that comprisesmultiple resistors that regulate temperatures independently over eachsmall area covered by each individual resistor.

FIG. 4A illustrates a cross-section of an embodiment of a PTC coating onan insulating yarn or filament.

FIG. 4B is a schematic of an embodiment of a mesh or fabric thatincorporates an insulating yarn or filament constructed as shown in FIG.4A.

FIG. 4C illustrates a cross-section of an embodiment of a PTC coating ona conductive yarn or filament.

FIG. 4D is a schematic of an embodiment of a mesh or fabric thatincorporates a conductive yarn or filament constructed as shown in FIG.4C.

FIGS. 5A and 5B are each a schematic cross section of a PTC ink andinterconnects deposited on a film (FIG. 5A) and subsequently laminated(FIG. 5B).

FIGS. 5C-5F are each a schematic cross section of a laminated HRM PTCthermal substrate positioned in thermal communication with a fabric ormesh.

FIG. 6 is a cross sectional view of a heater used in a body warming/painrelief application according to an embodiment.

FIG. 7 is a cross sectional view of a heater used in a body warming/painrelief application according to an embodiment.

FIG. 8 is a plan view of a used in a body warming/pain reliefapplication according to an embodiment.

While the present disclosure is susceptible to various modifications andalternative forms, specific embodiments or implementations have beenshown by way of example in the drawings and will be described in detailherein. It should be understood, however, that the disclosure is notintended to be limited to the particular forms disclosed. Rather, thedisclosure is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of an invention as defined by theappended claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows the relationship of the PTC ratio R_(T)/R₂₅ versustemperature T of a typical PTC ink composition. When the temperature Tis in excess of 70° C., the PTC ratio R_(T)/R₂₅ (also known as a“resistance magnification” or “resistivity magnification”) begins todecline. The PTC ratio R_(T)/R₂₅ is defined as the ratio between aresistance R_(T) at temperature T and the resistance R₂₅ at temperature25° C. The lower resistance at the onset of NTC leads to excessivecurrent flow and the heating element is overpowered. Therefore, the NTCtemperature region is a potential safety-risk temperature region.

FIG. 2 shows the relative resistance magnification of a high-resistancemagnification (HRM) PTC ink suitable for applications in the presentdisclosure. The HRM PTC ink exhibits the following properties: itsswitching temperature is at about 40° C.; its resistance magnification(or PTC ratio R_(T)/R₂₅) rises to about 200 within 30° C. of theswitching temperature; and it exhibits only PTC behavior 30° C. beyondthe switching temperature. That is, within a span of 30° C. above theswitching temperature, the current flowing through the HRM PTC ink isreduced by a factor of 200, thereby providing a self-regulatingmechanism by which the power consumption is reduced by 200. In fact,further investigation reveals that the HRM PTC ink has an upperresistance magnification greater than 200 above a temperature of 70° C.Furthermore, no NTC effect is observable 30° C. above the switchingtemperature, implying use of the HRM PTC ink is safe within thistemperature range.

For example, common commercially available PTC inks typically manifest aresistance multiplication of 10-15, as shown in FIG. 1. On the otherhand, the resistance magnification of an HRM PTC ink reaches 200 asshown in FIG. 2.

Moreover, the NTC effect is well above the switching temperature ascompared to the NTC effect depicted in FIG. 1. In addition, hysteresiseffects are absent, transition regions are short and resistance recoverytimes are short. Finally, the slope of the curve for the HRM PTC ink inFIG. 2 is steeper than that depicted in FIG. 1, which allows moretightly controlled temperature regulation.

These properties imply that the HRM PTC ink of FIG. 2 may be used inapplications where a PTC effect, along with a high resistancemagnification (i.e. power consumption reduction) are required betweenabout 40° C. and 70° C. The high resistance magnification can be greaterthan 50, or greater than 100, or greater than 150, in the temperaturerange of interest.

It follows that applications that require a PTC effect and highmagnification resistance in a different temperature range can use an HRMPTC ink with a) a switching temperature; b) PTC effect; and c) highresistance magnification in the required temperature range.

An example of an HRM PTC ink is disclosed in US Pat. Pub. No.20170327707, incorporated herein by reference. However, as discussedabove, any HRM PTC ink that exhibits substantially similarcharacteristics may be used. The requisite HRM PTC ink exhibits aswitching temperature, high resistance magnification and a PTC effectover the temperature range required for the application.

For example, the HRM PTC ink may comprise a first resin that provides afirst PTC effect in a first temperature range and a second resin thatprovides a second PTC effect in a second temperature range, wherein thesecond temperature range is higher than the first temperature range.

As an example, the double-resin HRM PTC ink may comprise about 10-30 wt% conductive particles; about 5-15 wt % of a first polymer resin; about5-15 wt % of a second polymer resin; about 40-80 wt % of an organicsolvent; and about 0-5 wt % other additives. The conductive particlescan be one of, or a mixture of: a metallic powder, a metal oxide, carbonblack and graphite. The first polymer resin may be a kind of crystallineor semi-crystalline polymer, such as polyurethane, nylon, and polyester.The second polymer resin may be a kind of non-crystalline polymer, suchas acrylic resin. The selection of the solvent is based on its properboiling point and the solubility of polymer resins since the polymerresins are completely dissolved in the organic solvent prior to blendingwith other components. Any organic, inert liquid may be used as thesolvent for the so long as the polymer is fully solubilized. Asexamples, the solvent may be selected from MEK, N-methyl pyrolidone(NMP), toluene, xylene, and the like. The other additives include adispersing/wetting additive and a rheology additive.

As an example of the double resin composition, the HRM PTC ink maycomprise about 5-15 wt % of a thermally active polymer resin-1 having amelting point of 30-70° C. and providing a first temperature coefficientcharacteristic in the first temperature range below 70° C.; about 5-15wt % thermally active polymer resin-2 having a melting point of 70-140°C. and providing a second positive temperature coefficientcharacteristic in the second temperature range above 70° C.; about 10-30wt % conductive particles; about 40-80 wt % organic solvent having aboing point higher than 100° C., the organic solvent being capable ofdissolve both the polymer resin-1 and polymer resin-2, and about 0-5 wt% additives. The additives may comprise dispersing additives, wettingadditives, and rheological additives, with the additives having enhanceddispersing/wetting and rheology properties. The first polymer resin maybe a kind of crystalline or semi-crystalline polymer, such aspolyurethane, nylon, and polyester. The second polymer resin may be akind of non-crystalline polymer, such as acrylic resin.

Thermal Substrate

In a thermal substrate comprising a substrate and an HRM PTC ink, theHRM PTC ink can provide the elimination of NTC and therefore avoidcatastrophic failure. Moreover, the high resistivity of the HRM PTC inkin a temperature window of 20° C. to 40° C. above the switch temperaturecan provide precise temperature self-regulation with rapidtime-to-temperature.

Non-limiting examples of a substrate include a fabric, a mesh, and afilm.

The present disclosure describes applications of the HRM PTC inkdescribed above that extends or eliminates the onset of the NTC effect,offers magnification factors greater than 15, 25, 50, 100, 150 or 200,and switches in the range of 0°−160° C. Such applications are thereforesafer, more reliable and dissipate minimal power at the switchtemperature. Moreover, the wide switch temperature range of HRM PTC inksoffers greater design flexibility and the steep temperature-resistancetransition enables tighter temperature control.

Thermal substrates that use HRM PTC ink may be created using variousmaterials—depending on the specific application. For example, foroutdoor wear, a nylon fabric may be used. For an industrial applicationthat requires a higher operating temperature, a woven glass fiber meshmay be used. Similarly, various substrates may be used depending on theparameters of the application. For example, for clothing wherelow-weight and flexibility are required, thermoplastic polyurethane(TPU), polyester or a natural fabric such as cotton or a cotton blend isappropriate.

In general, all-natural fibers, many polymer films and, in the case ofmeshes, metal wires are amenable to heating with a HRM PTC ink.

First Embodiment of a Thermal Substrate

In some embodiments, a thermal substrate may be made by deposition of aHRM PTC ink onto a fabric or mesh.

The HRM PTC ink may be deposited on the substrate by various techniques.For example, screen printing onto a substrate may be used successfullybecause of the favorable dispersion of the HRM PTC ink. Other suitabletechniques include gravure or rotogravure (e.g. “doctor blade”) methods.The HRM PTC ink may also be dispensed over simple or complex surfacesusing nozzles mounted on programmable robots or embedded in componentsby 3-D printing. Other methods of depositing a HRM PTC ink withsubstantial accuracy are known in the art.

Once the HRM PTC ink has been deposited on a fabric or mesh, silver orother conductive paste may be deposited on the substrate to createelectrical interconnects (e.g. contacts and bus lines) for use in heaterapplications. In some embodiments, other metals (e.g. metal foils orwires), metal alloys or electrically conductive materials such as, butnot limited to, aluminum, copper, nickel and alloys thereof, or highlyconductivity electronic polymers may be deposited on the substrate as apaste or ink to create interconnects. In all cases, interconnects can bedesigned for minimal length to lessen the possibility of cracking.

An HRM PTC ink is methodically deposited on a substrate such that theresulting circuit pattern provides for optimum power delivered by theresulting thermal substrate. For any given heating application, whereasthe switch temperature is determined by the composition of the HRM PTCink, the power delivered by the thermal substrate is determined by theHRM PTC ink's circuit pattern.

FIG. 3 depicts a printed circuit that comprises multiple deposits ofprinted HRM PTC ink. Each deposit of ink 380 acts as a resistor thatregulates temperatures independently over a small area covered by theindividual resistor 380. Each resistor 380 in a column is powered byline voltage busses 390 and interconnects 391. The printed circuitarises from deposition of the HRM PTC ink and conductive interconnectsonto the substrate, as described above.

Since the HRM PTC resistor 380 material typically has high sheetresistance, the power, P, is determined by arranging the printedresistors in parallel in a column on the substrate, as shown in FIG. 3.The power dissipated by a column, P_(col), is:P _(col) =V ² /R _(col),

where V is the applied voltage and R_(col) is the total resistance ofthe column. If the number of resistors in parallel within a column isn_(col) and the resistance of individual resistor 380 is R, theresistance of the column, R_(col), is:R _(col) =R/n _(col).

For a total of N columns (as depicted in FIG. 3), the total powerdissipated by the sheet, P, isP=n _(col) NV ² /R.

The resistors may have a length of from about 0.2 cm to about 10 cm. Thetemperature at each resistor is independently regulated. This circuitpattern allows independent temperature control of small areas,controlled power delivery and temperature uniformity, or non-uniformityif desired, over the surface of the substrate regardless of the localthermal load. The gap between discrete resistors may also be reduced tozero to form a contiguous line of resistors with identical behavior ofthe heater, i.e. local self-regulation in response to local thermal loadconditions. In all cases, the resistivity of the HRM PTC ink may beadjusted appropriately.

Second Embodiment of a Thermal Substrate

In other embodiments, the HRM PTC ink may be deposited on a thread,yarn, or mesh element for weaving into a fabric or mesh to create athermal fabric or mesh.

FIG. 4A illustrates a cross-section of an HRM PTC coating 420 on aninsulating thread, yarn, or filament 410. The HRM PTC ink is depositedas a coating 420 on the insulating thread, yarn, or filament 410 andpreferably sealed for electrical isolation on the outer surface with aninsulating polymer 430. Coating and sealing may be done by dipping,extrusion, or vapor deposition. Conduction of current is therefore alongthe length of the thread, yarn, or filament. In this configuration, theHRM PTC ink is formulated for low resistivity, while multiple coatedthreads, yarns or filaments may be connected in parallel.

In another embodiment shown in FIG. 4B, the HRM PTC ink 472 can bedeposited on a conductive thread, yarn, or filament 471 (e.g. such as acopper wire) and coated with another electrically conductive layer 473such as copper or silver. As above, there can be an optional insulatinglayer 474 around the conductive layer 473. In this case, the HRM PTC inkmay be formulated for high resistivity and electrical current flowsradially inward from the outer conductive layer 473 to the conductivethread 471.

FIG. 4C illustrates an example of how the coated threads 460 may bewoven into the weft of a fabric or mesh to form a thermal substrateusing an insulator as a thread, yarn, or filament. Wires 450 and 451carry supply voltage and are woven into the warp. Contact with theheater threads can be made by coating with pressure-sensitive adhesiveand subsequently simultaneously applying heat and pressure, pulsewelding, swaging, sealing with an overcoat or other means known in theart. The remaining threads 470 in the warp are standard fabric or meshmaterials, e.g. polyester.

FIG. 4D is a schematic of a mesh or fabric that incorporates aconductive yarn or filament constructed as shown in FIG. 4C. One wirecarrying supply voltage 480 makes contact with the outer conductor layerof the heater threads 490, which constitute the weft; the other wire 481makes contact with the inner conductor of the coated threads. Theremaining threads 495 are the customary fabric material. The innerconductors are exposed by stripping the HRM PTC ink from the threadswith solvent or mechanical means.

Third Embodiment of a Thermal Substrate

In yet another embodiment a thermal substrate 505 may be made bydepositing the HRM PTC ink 510 and conductive interconnects 511 onto apolymer film 520, as shown in FIG. 5A. The printed elements may besubsequently encapsulated by optionally laminating a second film 530 ofthe same composition (as that of film 520), resulting in a laminatedthermal substrate 535, as shown in FIG. 5B. Lamination may be achievedby using a pressure and temperature adhesive. Suitable substrate andencapsulation materials include, but are not limited to: polyester,polyimide, polypropylene, rubber, silicone, thermoplastic polyurethane,laminates, ethylene-vinyl acetate (EVA) adhesive film, acrylate adhesivefilm and silicon adhesive film, fabric, silicone, and polyethyleneterephthalate (PET). Additionally, the fabric or mesh heated by thethermal substrate 505 may have other layers of materials bonded to itsuch as, but not limited to: adhesive films, thermal barriers,reflective films, high or low emissivity films, absorptive films,alkaline resistant films, ground planes or EMI/RFI protective layers.

If the primary heat transfer mechanism is conduction, the laminatedthermal substrate 535 can be positioned in thermal communication with afabric or mesh 560 in order to heat the fabric or mesh 560, as shown inFIG. 5C. In the embodiment shown, the laminated thermal substrate 535may be merely positioned close to the fabric or mesh 560 to be incontact therewith. While laminated thermal substrate 535 (of FIG. 5B) isshown, thermal substrate 505 (of FIG. 5A) may be used in place of thelaminated thermal substrate 535.

Alternatively, the laminated thermal substrate 535 may be attached tothe fabric or mesh 560 by a fastener 570 (such as, but not limited to: arivet, snap, clasp or stud), as shown in FIG. 5D, or by various othermeans such as adhesives, sewing or removable clips. While laminatedthermal substrate 535 (of FIG. 5B) is shown in in FIG. 5C, the thermalsubstrate 505 (of FIG. 5A) may be used in place of the laminated thermalsubstrate 535.

If the primary mode of heat transfer is infrared radiation orconvection, the laminated thermal substrate 535 may not need to beproximate to the fabric or mesh 560. Then, an air gap 580 may beconfigured, as shown in FIG. 5E, between the laminated thermal substrate535 and the fabric or mesh 560. While laminated thermal substrate 535(of FIG. 5B) is shown, the thermal substrate 505 (of FIG. 5A) may beused in place of the laminated thermal substrate 535.

Whether the laminated thermal substrate 535 (or thermal substrate 505)is adjacent to the mesh or fabric 560 (as in FIG. 5C), fastened to themesh or fabric 560 (as in FIG. 5D), or separated from the mesh or fabric560 by an air gap 580 (as in FIG. 5E), an optional layer of material maybe used for thermal insulation, water proofing, etc. FIG. 5F illustrateda configuration where a laminated thermal substrate 535 is fastened to amesh or fabric 560, and placed near a layer of material 590, with an airgap 580. For example, in an embodiment, a heated jacket can have afabric lining that has an HRM PTC film attached thereto, along with awaterproof fabric that forms an outer layer of the jacket.

In various applications, the fabric or mesh heated by the thermal filmmay have a sensor positioned proximate to it or laminated in it.Furthermore, it may use a feedback loop to adjust its temperature basedon the sensor. In other applications, the HRM PTC ink itself may be usedas its own temperature sensor since it manifests such a strong andrepeatable relationship between resistance and temperature. In such anapplication, an auxiliary circuit may be configured to measure real-timeheater resistance for an accurate temperature integrated over the entirethermal film.

Application: Body Warming/Pain Relief

A flexible heater comprising a HRM PTC deposited on a flexible substratemay be used as an article for body warming and/or pain reliefapplications such as, but not limited to, heating pads, heat wraps,heated blankets, heated throws, heated body pillows and heated mattresspads.

The HRM PTC ink has a positive temperature coefficient (PTC) and aresistance magnification of at least 15 in a temperature range of atleast 20 degrees Celsius above a switching temperature of the HRM PTCink. The resistance magnification of the HRM PTC ink may be at least 20,30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180 or 200. In addition,the temperature range may be 25 degrees Celsius, 30 degrees Celsius, 35degrees Celsius or 40 degrees Celsius above the switching temperature.Furthermore, the switching temperature of the HRM PTC ink may be between0 and 160 degrees Celsius. As an example, the HRM PTC ink may be adouble resin ink that comprises: a first resin that provides a first PTCeffect in a first temperature range; and a second resin that provides asecond PTC effect in a second temperature range, wherein the secondtemperature range is higher than the first temperature range.

In some embodiments, the first temperature range is between 30 C-70 C.Suitable substrates for this application are low-weight and flexible,and can include for example, thermoplastic polyurethane (TPU) or fabricitself such as polyester blend or nylon.

The advantage of using HRM PTC heaters is the elimination of atemperature sensor, elimination of controller or power supply,elimination of physical connectors (e.g. wires), excellent temperatureuniformity and efficiency. The latter advantage arises from the HRM PTCink being formulated to switch at a desired level, as well as thelayout/design of the article. In addition, the article can achieveheating temperatures with lower voltage. In addition, the article can belaundered.

In some embodiments, the HRM PTC ink 600 is deposited onto a TPUsubstrate 610 using a method of screen printing, as shown in FIG. 6. Insome embodiments, the HRM PTC ink/TPU substrate assembly (i.e. theflexible heater) is cured using heat, and then encapsulated in anencapsulation material 700, as shown in FIG. 7. Suitable encapsulationmaterials for use in this application include a dielectric ink or otherthin film. In some embodiments, the encapsulated heater is inserted,sewn, or otherwise attached to a fabric or shell (that is placedadjacent to a user) to form the article for body warming and/or painrelief.

FIG. 8 is a plan view of a heater used in a body warming/pain reliefapplication according to an embodiment of the present invention. FIG. 8illustrates a thin film panel 800 comprising a HRM PTC ink 810 screenprinted onto a TPU substrate 815, cured with heat, and encapsulated witha dielectric ink (not shown). Panel 800 also comprises a series ofprinted conductive traces 820 that are screen printed onto the TPU,cured, and laminated with a dielectric ink. The conductive traces 820are designed to carry the electrical current. In FIG. 8, the conductivetraces 820 run perpendicular through the printed HRM PTC ink, whichcreates a plurality of individual resistors 810 that generate heat. Eachindividual resistor is also self-regulating due to the properties of theHRM PTC ink properties. Furthermore, the HRM effect of the ink relate tothe ability of each individual resistor resisting the electrical currentenough to prevent at least one of overheating, fires, and failure. Insome embodiments, printed silver traces are used.

In one example of body warming/pain relief application, a HRM PTC inkwas deposited onto a TPU substrate using a method of screen printing. Avoltage of 120 VAC was applied to the article, resulting in a wattdensity of between 5-10 watts/ft², or around 7 watts/ft². While thearticle can be any shape, in this example, it was square or rectangular.The square measured from 6 in×6 in to 24 in×24 in, or about 12 in×12 in.The rectangle measured from 6 in×12 in to 18 in×30 in, or about 12 in×24in. The self-regulating temperature of the double-switching ink wasabout 60° C., while the temperature of the article where applied to auser was about 50° C. to about 55° C. or about 52° C. In general, anarticle can be designed to obtain a range of self-regulatingtemperatures and watt densities, in order to achieve specific metricsrequired by a customer.

In a second example of body warming/pain relief application, a HRM PTCink is deposited onto a TPU substrate using a method of screen printing.A voltage of about 11.1 VDC was applied to the article, resulting in awatt density of between 60-70 watts/ft², or about 65 watts/ft². Whilethe article can be any shape, in this example, it was square, measuringfrom 6 in×6 in to 24 in×24 in, or about 12 in×12 in. The self-regulatingtemperature of the double-switching PTC ink was about 73° C., while thetemperature of the article where applied to a user was about 60° C. toabout 70° C. or about 65° C. In general, an article can be designed toobtain a range of self-regulating temperatures and watt densities, inorder to achieve specific metrics required by a customer.

While particular implementations and applications of the presentdisclosure have been illustrated and described, it is to be understoodthat the present disclosure is not limited to the precise constructiondisclosed herein and that various modifications, changes, and variationscan be apparent from the foregoing descriptions without departing fromthe spirit and scope of an invention as defined in the appended claims.

What is claimed is:
 1. An article comprising a heater, the heatercomprising: a double-resin ink having a positive temperature coefficient(PTC) deposited on a flexible substrate to form one or more resistors;wherein: the flexible substrate is thermal polyurethane, nylon, or apolyester blend; the double-resin ink comprises: a first resincomprising a crystalline or a semi-crystalline polymer; and a secondresin comprising a non-crystalline polymer, wherein the first resinprovides a first PTC effect in a first temperature range and the secondresin provides a second PTC effect in a second temperature range, thesecond temperature range being higher than the first temperature range;and the double-resin ink has a resistance magnification of at least 20in a temperature range of at least 20° C. above a switching temperatureof the double-resin ink, the resistance magnification being defined as aratio between a resistance of the double-resin ink at a temperature ‘T’and a resistance of the double-resin ink at 25° C.
 2. The article ofclaim 1, wherein the resistance magnification of the double-resin ink isat least
 50. 3. The article of claim 2, wherein the temperature range is30° C. degrees Celsius above the switching temperature.
 4. The articleof claim 1, wherein the switching temperature is between 0° C. and 160°C.
 5. The article of claim 1, wherein the double-resin ink comprises: a)5-15 wt % of a thermally active first polymer resin having a meltingpoint of 30° C.-70° C. and providing the first PTC effect in the firsttemperature range below 70° C., b) 5-15 wt % of a thermally activesecond polymer resin having a melting point of 70° C.-1400° C. andproviding the second PTC effect in the first temperature range above 70°C., c) 10-30 wt % of conductive particles, d) 40-80 wt % of an organicsolvent having a boiling point higher than 100° C., the organic solventbeing capable of dissolving both the first resin and the second resin,and e) 0-5 wt % of additives comprising a dispersive additive, a wettingadditive and a rheological additive, the additives having enhanceddispersing, wetting and rheological properties.
 6. The article of claim1, wherein the double-resin ink is deposited on to the flexiblesubstrate by screen printing.
 7. The article of claim 1, wherein theflexible substrate is thermal polyurethane.
 8. The article of claim 1,wherein the heater is encapsulated by a dielectric ink or a thin film.9. The article of claim 1, wherein the heater further comprises aplurality of conductive traces.
 10. The article of claim 9, wherein theplurality of conductive traces are each silver traces.
 11. A panelcomprising an encapsulated heater, the heater comprising: a double-resinink having a positive temperature coefficient (PTC) deposited on aflexible substrate to form one or more resistors, the double-resin inkcomprising a first resin comprising a crystalline or a semi-crystallinepolymer; and a second resin comprising a non-crystalline polymer;wherein: the flexible substrate is thermal polyurethane; the heater isencapsulated in a dielectric ink; and the double-resin ink has aresistance magnification of at least 20 in a temperature range of atleast 20° C. above a switching temperature of the double-resin ink, theresistance magnification being defined as a ratio between a resistanceof the double-resin ink at a temperature ‘T’ and a resistance of thedouble-resin ink at 25° C.
 12. The panel of claim 11, wherein the doubleresin ink is screen printed onto the flexible substrate.
 13. The panelof claim 11, wherein the encapsulated el heater further comprises aplurality of conductive traces.
 14. The panel of claim 13, wherein theplurality of conductive traces are laminated with a dielectric ink. 15.The panel of claim 14, wherein the plurality of conductive traces areeach silver traces.
 16. The panel of claim 11, wherein the resistancemagnification of the double-resin ink is at least
 50. 17. The panel ofclaim 11, wherein the switching temperature is between 0° C. and 160° C.18. The panel of claim 11, wherein the first resin provides a first PTCeffect in a first temperature range and the second resin provides asecond PTC effect in a second temperature range, the second temperaturerange being higher than the first temperature range.
 19. The panel ofclaim 18, wherein the double-resin ink comprises: a) 5-15 wt % of athermally active first polymer resin having a melting point of 30°C.-70° C. and providing the first PTC effect in the first temperaturerange below 70° C., b) 5-15 wt % of a thermally active second polymerresin having a melting point of 70° C.-1400° C. and providing the secondPTC effect in the first temperature range above 70° C., c) 10-30 wt % ofconductive particles, d) 40-80 wt % of an organic solvent having aboiling point higher than 100° C., the organic solvent being capable ofdissolving both the first resin and the second resin, and e) 0-5 wt % ofadditives comprising a dispersive additive, a wetting additive and arheological additive, the additives having enhanced dispersing, wettingand rheological properties.